Slow Adaptation of Modulation and Coding for Packet Transmission

ABSTRACT

Systems and methods for performing MCS adaptation are provided. In some cases, the network performs MCS adaptation based on received NACKs. In other cases, the mobile station determines an MCS based on channel quality measurements, and feeds back the MCS adaptation decision to the network. In either case, NACK-only feedback may be implemented to reduce interference.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation which claims benefit of and priorityto U.S. patent application No. 11/690,615 filed Mar. 23, 2007, by ZhijunCai, et al. entitled “Slow Adaptation of Modulation and Coding forPacket Transmission,” (32181-US-PAT-4214-06300) which is incorporated byreference herein as if reproduced in its entirety.

FIELD OF APPLICATION

The application relates to packet transmission such as real-time lowrate transmission, over a wireless link.

BACKGROUND

HARQ (Hybrid Automatic Repeat reQuest) is widely used in the LTE (longterm evolution) 3GPP TR 25.814. Multiple fast retransmissions can helppacket reception especially for the UEs (user equipment) at locationswith poor channel conditions. However, for a real-time low-rate service,such as VoIP (Voice over IP), the number of retransmissions is limiteddue to the delay budget and voice frame rate. In a fast fadingenvironment, fast CQI (channel quality indication) feedback can be usedby the UE to signal channel quality to the base station. The basestation uses this information to perform fast AMC (adaptive modulationand coding) by selecting an MCS (modulation and coding scheme) for theparticular UE. However, fast CQI is undesirable due to the significantuplink overhead caused by the possible large number of UEs for suchservices (e.g., VoIP UEs). An alternative to using fast AMC is to relyon retransmissions to compensate for the fast fading.

BRIEF DESCRIPTION OF DRAWINGS

Embodiments will now be described with reference to the attacheddrawings in which:

FIG. 1 is a diagram showing an example of a resource block indexconcept;

FIG. 2 is a diagram showing an example of NACK-only feedback;

FIG. 3 contains signal diagrams for conventional ACK/NACK feedback andNACK-only feedback;

FIG. 4 is a flowchart of a method of performing NACK-only feedback;

FIG. 5 is a flowchart of a method of performing MCS adaptation based onreceived NACKs;

FIG. 6 is a flowchart of another method of performing MCS adaptationbased on received NACKs;

FIG. 7 is a flowchart of a method of performing UE assisted MCSadaptation;

FIG. 8 is a block diagram of a network within which embodiments of theapplication may be implemented;

FIG. 9 is a block diagram of a UE within which embodiments of theapplication may be implemented; and

FIGS. 10, 11 and 12 contain block diagrams of receivers and networkcomponents that implement AMC adaptation and/or NACK-only feedback.

DETAILED DESCRIPTION

A broad aspect provides a method comprising: transmitting packets to areceiver using an MCS (modulation and coding scheme); receiving NACKs(negative acknowledgement) in respect of packets transmitted to thereceiver; determining an updated MCS (modulation and encoding scheme)used to transmit subsequent packets to the receiver as a function of thereceived NACKs.

Another broad aspect provides a method comprising: a receiver receivingpackets sent to the receiver over a wireless channel; the receivermaking a channel quality measurement in respect of the wireless channel;the receiver making an MCS adaptation decision based on the channelquality measurement; the receiver feeding back the MCS adaptationdecision in a slow rate manner.

Another broad aspect provides an arrangement of one or more wirelessnetwork components comprising: at least one antenna; a transmitter thattransmits packets to a wireless device using an MCS (modulation andcoding scheme); a receiver that receives adaptation decisions from thewireless device; an MCS adaptor that updates the MCS used to transmitsubsequent packets to the wireless device based on the adaptationdecisions received from the wireless device.

Another broad aspect provides arrangement of one or more wirelessnetwork components comprising: at least one antenna; a transmitter thattransmits packets to a wireless device using an MCS (modulation andcoding scheme); a receiver that receives NACKs (negativeacknowledgements) in respect of packets sent to the wireless device; anMCS adaptor that updates the MCS used to transmit to the wireless devicebased on the NACKs received the wireless device.

Another broad aspect provides a wireless device comprising: at least oneantenna; a receiver that receives packets; a channel quality measurementfunction that determines an average channel quality of a wirelesschannel over which the packets were received; an MCS (modulation andcoding scheme) adaptor that makes an MCS adaptation decision as afunction of the average channel quality of the wireless channel; atransmitter that transmits the MCS adaptation decision.

In addition, some of the methods described herein lend themselves toimplementation in software stored on a computer readable medium. Furtherembodiments provide such a computer readable medium upon which is storedcomputer readable instructions to implement one or more of the methods.

Embodiments of the application provide for slow resource control used ina manner that “fits” the UE's geometry in order to limit the number ofretransmissions. In the following, slow resource control for twodifferent MCS assignment mechanisms will be described, namelyindependent MCS allocation, and groupwise MCS allocation.

In embodiments employing independent MCS, each UE's MCS is independentlymaintained in the UE and base station (such as an Enhanced-Node-B (ENB)(an LTE base station)). The User-plane transmission is independent foreach UE.

In embodiments employing groupwise MCS allocation, UE groupings aredefined, each UE grouping having a group property. In some embodiments,each group property is defined by a common MCS. The group size can befixed or dynamic. In some embodiments, a group property is defined bycommon MCS in combination with a common RV (redundancy version). Twogroups with the same MCS as reflected by the modulation and code rate,may employ coding with different coding properties. A simple example ofa set of group property definitions is listed in Table 1:

TABLE 1 Group property Modulation Coding Group 1 QPSK 0.5 Group 2 QPSK0.75 Group 3 16QAM 0.5 Group 4 16QAM 0.75

In this example, there are four groups. Each group has a respectivegroup property defined by the modulation and coding. The actualdefinition of a set of possible group properties is implementationspecific.

In the event a limited size of each group is imposed, there may bemultiple groups that have the same group property. UEs with the samegroup property have similar average path loss (similar geometry) and QOSrequirements (delay, jitter, BLER).

Initial MCS Assignment

Initial MCS assignment is the assignment of an MCS at the start of acommunication. For independent MCS allocation, the network will firstassign each UE to an initial MCS. For groupwise MCS allocation, thenetwork will assign a group to the UE, the group having an associatedMCS. In either case, the MCS might be selected to have properties thatmatch the UE's current geometry and traffic properties.

In some embodiments, a UE requests the initial setting by reporting itscurrent channel quality (for example average SNR condition) to the ENB.The ENB decides which MCS or Group is best suited to the UE and assignsthe UE to that MCS/Group.

In some embodiments, the ENB assigns the UE to an initial MCS or aninitial Group as a function of an uplink measurement. Note that thedownlink MCS and uplink MCS may be different for a single UE. Theinitial assignment may be different for the DL and the UL (since thechannel may be asymmetric). In one embodiment, the network may simplyinitially assign all UE's to the lowest modulation and codingrequirement. The initial assignment can be signaled in any appropriatemanner. In a specific example, layer 3 signaling via a RRC (radioresource control) procedure at the call setup stage is employed.

Resource Block Assignment

In some embodiments, an OFDM (orthogonal frequency divisionmultiplexing) resource is used to define resource blocks. A resourceblock includes a set of sub-carriers offset in frequency dimension and aset of OFDM symbol durations in the time dimension. The locations of agiven resource block (or a resource block set) can be arbitrarilydefined. They may be distributed in time and/or frequency, or contiguousin time and/or frequency. A specific example of a resource blockallocation is shown in FIG. 1. In FIG. 1, an OFDM resource consisting ofOFDM sub-carriers in the frequency dimension 200 and OFDM symbols in thetime dimension 202 is shown. A particular point in this two dimensionalspace can be used as a resource block allocation start index for a givengroup. An example of this is indicated at 204. Note that a resourceblock allocation can involve contiguous sub-carriers, or it can involvesub-carriers that are spread throughout an available OFDM bandwidth. Aresource index can be used to refer to a particular resource block orresource block set.

More generally, resource blocks can be defined using any appropriate airinterface technology, for example WCDMA (wideband code division multipleaccess) or MC-CDMA (multi-carrier code division multiple access) to namea few other specific examples.

In some embodiments, there are K resource blocks assigned per group. Kcan be constant across groups, or different across groups. In someembodiments, layer 3 or layer 2 signaling can be used to signal anassignment of resource blocks to a given group. This will also associatethe group's group property (MCS and RV if used) with that resourceassignment.

Notification for New Data Transmission

The notification of a new packet transmission is performed throughphysical layer signaling. A new packet transmission is the firsttransmission of a given packet, as opposed to subsequent HARQretransmissions. This signaling may be implemented using layer 1signaling or implicitly derived by the persistent scheduling. If done bylayer 1 signaling, a downlink L1 signaling portion (part of the overalllayer 1 signaling) can be used to signal the notification. Specificexamples of new packet notifications are given below.

In embodiments with independent MCS allocation, the Layer 1 signalingmight for example include a UE identifier and a resource index, theresource index indicating where in the transmit resource the particularUE's content will be located. This might refer to a resource block orresource block set for example. In some embodiments, the resource indexalso implicitly indicates the MCS state. For example, if a set ofresource blocks is collectively assigned a particular MCS, thenassignment of a UE to one of those resource blocks implies thatparticular MCS is being used for that UE.

In embodiments with groupwise MCS allocation, the following is anexample of information that might be transmitted for the purpose ofnotification of a new packet transmission:

1) Group ID: this implies: a) there will be User plane data for thegroup; b) the modulation and coding scheme;

2) Bitmap: this tells which UE(s) in the identified group will have datawithin the following data transmission; such a bitmap might for exampleinclude a respective bit for each UE in the group having the identifiedGroup ID, with the bit set to a first state (one or zero) to indicatethat data is included for the UE, and a second state (zero or one) toindicate that there is no data included for the UE;

3) The Resource Index: this identifies the transmission resources (forexample which resource blocks) that are being allocated to the group. Insome embodiments, the RB allocation for each group is fixed via theinitial signaling, for example initial layer 3 signaling. Signaling theresource index for new packet notification using L1 signaling need notbe performed in such instances.

NACK-Only Feedback

The Rel 6 HSDPA retransmission mechanism 3GPP TS 25.321 employs anACK/NACK (acknowledgement/negative acknowledgement) based feedbacksystem which is expected to cause large amounts of feedback for theVoIP. In such a system, each UE signals an ACK or a NACK for eachtransmission it receives to signal success or failure. In order toreduce feedback, a NACK-based feedback mechanism is provided in whichthe UE transmits a NACK when a received packet is in error and transmitsnothing when the received packet is decoded correctly. This reducesuplink interference significantly when compared with the ACK/NACK basedsystem.

In some embodiments, a simple ON/OFF keyed scheme on the reverse linkcan be applied assuming the UE has DTX (discontinuous transmission)capability. More specifically, in a UE feedback channel, a signal thatuses some amount of energy (might represent a logical +1 or a −1 forexample) is used to indicate NACK, and no energy is transmittedotherwise.

An example of NACK-only feedback is shown in FIG. 2. A set of firstpacket transmissions is indicated at 304,308,310. It is assumed thatpacket 304 is not received correctly and as such the UE transmits a NACK312. Packet 306 is a re-transmission that is then properly received bythe UE. The dotted lines at 314 are representative of the fact thatnothing is transmitted when a packet is properly received.

In some embodiments, to maintain a similar level of reliability assystems with ACK/NACK, the power used to transmit the NACK bits isincreased, for example doubled. See for example FIG. 3 which shows asignal design for NACK-only feedback. Conventional ACK/NACK feedback isindicated at 100, this including a first signal 102 for ACK, and asecond signal 104 for NACK. NACK-only feedback is indicated at 110. Thisincludes DTX 106 (i.e. transmit nothing) for ACK and signal for NACK108. In this example, the power of the NACK in the NACK-only feedback110 is double that in the ACK/NACK feedback with the result that thedistance in signal space between the ACK and the NACK in ACK/NACK signaldesign 100 is the same as the distance between the DTX and the NACK forthe NACK-only signal design 110, thereby ensuring the same reliability.The ENB looks for the NACK feedback transmission from a given UE at apre-determined time. If the ENB does not detect enough energy toconclude a valid NACK transmission was received, it is assumed no NACKwas transmitted, and that the UE correctly received the packet. If theENB does detect enough energy to conclude a NACK was transmitted, thenthe ENB will schedule the packet retransmissions.

A flowchart of an example implementation of NACK-only feedback is shownin FIG. 4. If a packet is received correctly, yes path step 4-1, thennothing is transmitted in response, step 4-2. If a packet is receivedincorrectly, no path step 4-2, then a NACK is transmitted at step 4-3.

Slow Adaptive MCS Change

Due to the UE's mobility capability, the UE's geometry may change withrespect to time. In some embodiments, slow adaptive MCS/grouping isapplied for voice UEs. The following are two examples of how this can beapplied. Adaptation is “slow” in the sense that no attempt to track afast-fading channel is made. Tracking a fast-fading channel might forexample require channel estimation every 2 ms. Rather, the UE tracks theaverage channel condition over a longer window, for example over awindow of 400 ms or greater.

1) Network Assisted

In the network assisted adaptive MCS method, the network monitors theUE's NACKs. This might for example involve determining the NACK rate orsimilar quantity. Based on this, the network slowly changes the UE'sassigned MCS/group.

A flowchart of a network assisted adaptive MCS method is shown in FIG.5. At step 5-1, packets are transmitted as part of a real-timetransmission over a wireless channel. At step 5-2, a NACK is receivedfor each packet transmitted to the receiver that was not receivedsuccessfully. At step 5-3, an MCS used to transmit subsequent packets tothe receiver is updated as a function of the received NACKs.

For example, consider a UE that is initially assigned M=16 QAM, C=0.75.If, after a period of time, the network detects a NACK rate which islarger than a transition threshold, the network moves the UE to a moreconservative MCS (for example, with M=QPSK, C=0.5). In the event themost conservative MCS is already being used, in some embodiments, thepower used to transmit to that user is increased. The following is anexample of a specific algorithm to implement this.

Define:

N(j): the number of NACKs received from a particular UE j over a slidingwindow for accumulating the NACKs;

Λ: size of the sliding window for accumulating NACKs;

N(MAX): first threshold for moving a UE to a more conservativemodulation and coding and/or power level—there can be a singlethreshold, or multiple thresholds; thresholds can be the same ordifferent for different UEs;

N(MIN): second threshold for moving a UE to a more aggressive modulationand coding and/or power level—there can be a single threshold, ormultiple thresholds; thresholds can be the same or different fordifferent UEs.

As an example of specific values for these parameters, slidingwindow=400 ms, N(MAX)=20; N(min)=3. However, the actual values used canbe selected on an implementation specific basis.

The procedure in the ENB will now be described with reference to theflowchart of FIG. 6. To begin, the number of NACKs received from acertain UE, say UE j, is counted over a time period that might forexample be a sliding window as described above, at step 6-1.

If in any duration Λ, N(j)>N(MAX) (yes path step 6-2), the UE is moved amore conservative MCS (step 6-3). In some embodiments, if no moreconservative MCS is available, the power level may be increased. Theassignment may also be based on RRM (radio resource management)considerations.

Similarly, if in any duration Λ, N(j)<N(MIN) (yes path step 6-4), the UEis assigned a more aggressive MCS (step 6-5). This may also be based onRRM considerations.

For groupwise MCS assignment, a change in the MCS will mean a change inthe group to which the UE is assigned.

In network assisted adaptive MCS, there is no requirement for CQIfeedback from the UE since the adaptive MCS approach does not use theCQI feedback to make adaptation decisions. Assuming no CQI feedback issent, the UE's battery life can be extended.

The above approach to slow adaptive MCS change can be implemented incombination with the NACK-only feedback. However, it can also be usedwith any feedback mechanism that includes at least NACKs, for examplesystems employing conventional ACK/NACK feedback. The number of NACKscounted would be the same in either case.

In some embodiments, the network assisted adaptation further involvessignaling to the receiver about the updated MCS. In other instances, thereceiver may determine the updated MCS without such signaling, forexample by using blind detection.

2) UE Assisted

In a UE assisted adaptive MCS method, the UE measures its own receptionquality. If the UE determines the reception quality is sufficientlygood, it requests to be moved to a more aggressive MCS using an uplinksignaling. If the UE determines the reception quality is very poor, itrequests to be moved to a more conservative MCS. Any appropriatesignaling scheme can be employed. No CQI feedback need be implemented.

In some embodiments, the signaling for the request is Layer 1 signalingwith 2 bit information to show the MCS change (2 bits to signal fourstates: up 1 level, down 1 level; maintain the same; unused). In someembodiments, the frequency of performing this signaling can be veryslow, e.g., every 600 ms, and this can reduce the uplink overheadcompared to the employment of full CQI transmission.

In some embodiments, in either case 1 (Network Assisted) or case 2 (UEAssisted), the network may choose not to move a UE to a more aggressiveMCS/group. For example, if a particular UE has a high QoS requirement,then a transition to a more aggressive MCS/group may not be appropriate.The network might, for example, signal the decision to the UE by eitherRRC signaling or Layer 2 signaling or physical layer indications.

A flowchart of a method of UE assisted MCS adaptation is shown in FIG.7. The receiver receives a sequence of packets as part of a real-timetransmission at step 7-1. At step 7-2, the receiver makes channelquality measurement in respect of a channel over which the packets werereceived. The receiver makes an MCS adaptation decision based on thechannel quality measurement at step 7-3. Finally, the receiver feedsback to MCS adaptation decision at step 7-4.

While a particular application of the methods and systems describedherein is to Vol P traffic, more generally, they can be applied to anyreal-time transmission over a wireless link such as streaming video,Instant messaging, real-time gaming, etc.

Referring now to FIG. 10, shown is a block diagram of an examplecommunication system 40-1 for generating NACK-only feedback. Thecommunication system 40-1 has a wireless network 20-1, a mobile device10-1 (previously referred to as a UE), and other mobile devices 30-1;the communication system 40-1 may have other components, but they arenot shown for sake of simplicity. For example, the mobile device and thenetwork will each have transmitters and receivers, one or more antennaseach. The mobile device 10-1 has a wireless access radio 16-1, aprocessor 17-1, and a NACK-only feedback generator. The mobile device10-1 may have other components, but they are not shown for sake ofsimplicity. The other mobile devices 30-1 may each have componentssimilar to those of the mobile device 10-1. Alternatively, some or allof the other mobile devices 30-1 may have different components thanthose of the mobile device 10-1. The wireless network 20-1 has aNACK-only feedback processor 22.

In operation, the mobile device 10-1 communicates with the wirelessnetwork 20-1 using its wireless access radio 16-1. The wirelesscommunication is over a wireless connection 19-1 between the mobiledevice 10-1 and the wireless network 20-1. The other mobile devices 30-1may similarly communicate with the wireless network 20-1 over respectivewireless connections (not shown). The communication with the wirelessnetwork 20-1 might for example be telephony, or other forms ofcommunication such as email. The NACK-only feedback generator 15generates NACKs when packets are received incorrectly, and generatesnothing when packets are received correctly. In the wireless network20-1, the NACK-only feedback processor 22 processes the NACK-onlyfeedback, and performs retransmissions as appropriate. Of course, a NACKthat is transmitted may not necessarily be received as such—the effectsof the channel may cause this to be interpreted as if nothing wastransmitted; in addition, during a period that nothing is transmitted toindicate acceptable transmission, it is possible that the effects of thechannel may cause this to be interpreted as if a NACK was transmitted.

In the illustrated example, the NACK-only feedback generator 15 isimplemented as software and is executed on the processor 17-1. However,more generally, the NACK-only feedback generator 15 may be implementedas software, hardware, firmware, or any appropriate combination thereof.Similarly, the NACK-only feedback processor 22 may be implemented assoftware, hardware, firmware, or any appropriate combination thereof.

Referring now to FIG. 11, shown is a block diagram of an examplecommunication system 40-2 for implemented UE assisted MCS adaptation.The communication system 40-2 has a wireless network 20-2, a mobiledevice 10-2 (previously referred to as a UE), and other mobile devices30-2; the communication system 40-2 may have other components, but theyare not shown for sake of simplicity. The mobile device 10-2 has awireless access radio 16-2, a processor 17-2, a channel qualitymeasurement generator 18, and an MCS adaptation decision generator 21.The mobile device 10-2 may have other components, but they are not shownfor sake of simplicity. The other mobile devices 30-2 may each havecomponents similar to those of the mobile device 10-2. Alternatively,some or all of the other mobile devices 30-2 may have differentcomponents than those of the mobile device 10-2. The wireless network20-2 has an MCS adaptor 24 that performs MCS adaptation based onadaptation decisions received from the UE.

In operation, the mobile device 10-2 communicates with the wirelessnetwork 20-2 using its wireless access radio 16-2. The wirelesscommunication is over a wireless connection 19-2 between the mobiledevice 10-2 and the wireless network 20-2. The other mobile devices 30-2may similarly communicate with the wireless network 20-2 over respectivewireless connections (not shown). The communication with the wirelessnetwork 20-2 might for example be telephony, or other forms ofcommunication such as email. The channel quality measurement generator18 determines a channel quality measurement in respect of the wirelesschannel over which packets are received. The MCS adaptation decisiongenerator 21 takes this channel quality measurement and makes an MCSadaptation decision and feeds this back to the wireless network 20-2.

In some embodiments, the UE assisted MCS adaptation is implemented onlyfor real-time services, with conventional CQI feedback implemented forother services.

In the illustrated example, the channel quality measurement generator 18and the MCS adaptation decision generator 21 are implemented as softwareand is executed on the processor 17-2. However, more generally, thechannel quality measurement generator 18 and the MCS adaptation decisiongenerator 21 may be implemented as software, hardware, firmware, or anyappropriate combination thereof. The MCS adaptor 24 may for exampleinclude software to process the adaptation decision and hardware toperform the actual modulation in accordance with the selected MCS.However, more generally, these functions may be implemented as software,hardware, firmware, or any appropriate combination thereof.

Referring now to FIG. 12, shown is a block diagram of an examplecommunication system 40-3 for implementing network assisted MCSadaptation. The communication system 40-3 has a wireless network 20-3, amobile device 10-3 (previously referred to as a UE), and other mobiledevices 30-3; the communication system 40-3 may have other components,but they are not shown for sake of simplicity. The mobile device 10-3has a wireless access radio 16-3, a processor 17-3. The mobile device10-3 may have other components, but they are not shown for sake ofsimplicity. The other mobile devices 30-3 may each have componentssimilar to those of the mobile device 10-3. Alternatively, some or allof the other mobile devices 30-3 may have different components thanthose of the mobile device 10-3. The wireless network 20-3 has an MCSadaptor 23 that performs MCS adaptation based on NACKs.

In operation, the mobile device 10-3 communicates with the wirelessnetwork 20-3 using its wireless access radio 16-3. The wirelesscommunication is over a wireless connection 19-3 between the mobiledevice 10-3 and the wireless network 20-3. The other mobile devices 30-3may similarly communicate with the wireless network 20-3 over respectivewireless connections (not shown). The communication with the wirelessnetwork 20-3 might for example be telephony, or other forms ofcommunication such as email. The mobile device 10-3 generates NACKs whenpackets are received incorrectly. The device may or not additionallygenerate an ACK in respect of each packet that is correctly receiveddepending on whether or not NACK-only feedback is implemented. In thewireless network 20-1, the function 23 processes the received NACKs andmakes MCS adaptation decisions based on the received NACKs.

In some embodiments, the MCS adaptation based on NACKS is implementedonly for real-time services, with conventional CQI based MCS adaptationimplemented for other services.

In the illustrated example, the MCS adaptor 23 includes software forprocessing the received NACKs, and hardware for performing modulation inaccordance with the selected MCS. However, more generally, thesefunctions may be implemented as software, hardware, firmware, or anyappropriate combination thereof.

The wireless networks of FIGS. 10, 11, 12 are not shown with anyspecific components other than those specifically involved inimplementing embodiments. The structure of the network will vary fromone implementation to the next. However, it is to be understood that thewireless network would have any appropriate components suitable for awired and/or wireless network. The components are implementationspecific and may depend on the type of network.

FIG. 8 is an exemplary environment in which a wireless communicationsystem 400 in accordance with some embodiments may be practiced.Communications between illustrated network elements can be implementedusing the above-summarized slow MCS adaptation methods. The exemplarywireless communication system 400 includes a plurality of host services(three shown, 402, 404, and 406), each of which may have a plurality ofservices such as, but not limited to, e-mail, calendar, Internet webbrowser, and other applications, available to their subscribers. In thisparticular example, the host services 402, 404, and 406 are typicallyconfigured as servers, each containing at least one processor, a storagemeans and each using a network interface over which communications witha communication network 408 such as the Internet can be effectuated. Thehost services 402, 404 and 406 send and receive messages overcommunications network 408 to and from wireless router system 410allowing communication between the host services 402, 404, and 406 andthe wireless router system 410.

The wireless router system 410 is connected to a plurality of wirelessnetworks (three shown, 414, 416, and 418), each of which may support aplurality of mobile devices (one in each wireless network is shown, 420,422, and 424). The wireless networks 414, 416, and 418 may be a cellulartelephone network, such as a global system for mobile communication(GSM) network, or a code division multiple access (CDMA) network, atwo-way paging network, a short range wireless network such asBluetooth™, an IEEE 802.11 compliant network, and others alike. Themobile devices 420, 422, and 424 are devices compatible with thecorresponding wireless network.

Mobile communications devices 420, 422 and 424 are two-way communicationdevices with advanced data communication capabilities having thecapability to communicate with other mobile devices or computer systems,such as host services 402, 404, 406, through a network of transceiverstations, including wireless router 410 and communication network 408.The mobile communication devices 420, 422 and 424 may also have thecapability to allow voice communication. Depending on the functionalityprovided, it may be referred to as a data messaging device, a two-waypager, a cellular telephone with data messaging capabilities, a wirelessInternet appliance, or a data communication device (with or withouttelephony capabilities). The preceding list is not meant to beexhaustive; the embodiments described herein can be practiced with anytype of mobile device, whether listed above or not. In the example shownin FIG. 8, mobile communications devices 420, 422 and 424 each contain aprocessor, a radio, an information storage means and at least onesoftware module adapted to perform tasks. In some embodiments, mobilecommunications devices 420, 422 and 424 are capable of sending andreceiving messages using the radio. Also in some embodiments , the atleast one software module includes an event generator module, adapted togenerate events, and a communications module, adapted to send andreceive messages using the mobile communications device's radio.

Mobile communications devices are generally capable of communicatingover multiple communication channels. For example, short message service(SMS) messages arrive over the voice communication channel, whereasemail messages arrive over a data communication channel. As explainedabove, the mobile communications device 420 includes modules, softwarefor example, which are adapted to perform various tasks when executed inmobile communications device 420's processor. In one embodiment, themobile communications device 420 contains both a communication moduleand an event generator module. The communication module is adapted toexecute in mobile communications device 420's processor and incooperation with the mobile communications device 420's radio is capableof sending and receiving messages. The event generator module is alsoadapted to execute in mobile communications device 420's processor andis capable of generating events in one of two ways: user generatedevents and device generated events. User generated events include suchthings as the user of mobile communications device 420 opening amessaging application resident in mobile communications device 420, suchas an email application, the user of mobile communications device 420rolling a wheel input device, such as a thumbwheel, the user of mobilecommunications device 420 pressing a key on mobile communications device420's keyboard, the user of mobile communications device 420 logging into mobile communications device 420 or the user of mobile communicationsdevice 420 electing to maintain an active session by responding to aprompt from mobile communications device 420. Device generated eventsinclude such things as the expiry of a timer, mobile communicationsdevice 420 generating a ping message to keep a session alive with thenetwork or mobile communications device 420 commencing a data session,such as a PDP context, with a network.

One of the primary purposes of host services 402, 404 and 406 is toprocess information received from other sources, such as mail servers(not shown) and mobile communications devices 420, 422, 424, and sendthe information on to the appropriate recipient, typically a differenthost service 402, 404, 406, mail server or mobile communications device420, 422 or 424. Host services 402, 404 and 406 are configured to sendand receive email messages and as such typically communicate with a mailserver. Mail servers could include for example a Microsoft® Exchange®server, a Lotus® Domino® server, a Novell® GroupWise® server, an IMAPServer, a POP Server or a webmail server or any other mail server aswould be understood by those in the art. The host services 402, 404 and406 also contain a software module, which executes in their processor toachieve the desired sending and receiving of messages as well as theappropriate processing of information. In some embodiments the softwaremodule of each host service 402, 404, 406 is a messaging module, themessaging module is adapted to receive messages from at least oneexternal mail server, send messages to mobile communications devices420, 422, 424, receive messages from the same mobile communicationsdevices and send messages to the at least one external mail server(s).The at least one external mail server(s) could also be at least onemobile data server(s) for example. The wireless router system 410 mayalso be directly connected to a host service, such as a local service412, without the communication network 408. In another embodiment, it ispossible for host services 402, 404 and 406 to communicate directly withmobile communications devices 420, 422 and 424. In this embodiment, hostservices 402, 404 and 406 must be capable of addressing communicationsto mobile communications devices 420, 422 and 424 without the aid of thewireless router system 410.

In the environment described in FIG. 8, messaging occurs between mobilecommunications devices 420, 422 and 424 and host services 402, 404 and406. It is possible for mobile communications devices 420, 422 and 424to send messages to and receive messages from host services 402, 404 and406. As an example, when a message is received by any one of hostservices 402, 404, 406, the intended recipient, mobile communicationsdevices 420, 422 and 424 is informed by the host service 402, 404 and406 that a message has arrived which needs to be retrieved by way of anenable message. Host service 402, 404 and 406 may send a plurality ofenable messages to mobile communications device 420, 422 and 424 or hostservice 402, 404 and 406 may choose to send one enable message untilmobile communications device 420, 422 and 424 fetches the pendingmessage(s). A fetch command is issued by the mobile communicationsdevice 420, 422 and 424 upon the generation of an event by an eventgenerator after an enable message has been received and is sent to hostservice 402, 404 and 406. The generated event and the enable message areindependent and neither one influences the occurrence or likelihood ofthe other. When host service 402, 404 and 406 receives a fetch command,host services 402, 404 and 406 will send the pending message or messagesto mobile communications device 420, 422 and 424 which issued the fetchcommand. Both the enable messages and the fetch message may or may notcontain message identifiers. A message identifier uniquely identifies amessage for mobile communications devices 420, 422 and 424 and allowsmobile communications devices 420, 422 and 424 to retrieve specificmessages. The host service 402, 404, 406 may send all pending messagesshould multiple messages be pending for the mobile communications device420, 422 and 424 which issued the fetch command.

Referring now to FIG. 9, shown is a block diagram of a mobilecommunication device 700 that may implement mobile device relatedmethods described herein. It is to be understood that the mobile device700 is shown with very specific details for example purposes only.

A processing device (a microprocessor 728) is shown schematically ascoupled between a keyboard 714 and a display 726. The microprocessor 728controls operation of the display 726, as well as overall operation ofthe mobile device 700, in response to actuation of keys on the keyboard714 by a user.

The mobile device 700 has a housing that may be elongated vertically, ormay take on other sizes and shapes (including clamshell housingstructures). The keyboard 714 may include a mode selection key, or otherhardware or software for switching between text entry and telephonyentry.

In addition to the microprocessor 728, other parts of the mobile device700 are shown schematically. These include: a communications subsystem770; a short-range communications subsystem 702; the keyboard 714 andthe display 726, along with other input/output devices including a setof LEDS 704, a set of auxiliary I/O devices 706, a serial port 708, aspeaker 711 and a microphone 712; as well as memory devices including aflash memory 716 and a Random Access Memory (RAM) 718; and various otherdevice subsystems 720. The mobile device 700 may have a battery 721 topower the active elements of the mobile device 700. The mobile device700 is in some embodiments a two-way radio frequency (RF) communicationdevice having voice and data communication capabilities. In addition,the mobile device 700 in some embodiments has the capability tocommunicate with other computer systems via the Internet.

Operating system software executed by the microprocessor 728 is in someembodiments stored in a persistent store, such as the flash memory 716,but may be stored in other types of memory devices, such as a read onlymemory (ROM) or similar storage element. In addition, system software,specific device applications, or parts thereof, may be temporarilyloaded into a volatile store, such as the RAM 718. Communication signalsreceived by the mobile device 700 may also be stored to the RAM 718.

The microprocessor 728, in addition to its operating system functions,enables execution of software applications on the mobile device 700. Apredetermined set of software applications that control basic deviceoperations, such as a voice communications module 730A and a datacommunications module 730B, may be installed on the mobile device 700during manufacture. In addition, a personal information manager (PIM)application module 730C may also be installed on the mobile device 700during manufacture. The PIM application is in some embodiments capableof organizing and managing data items, such as e-mail, calendar events,voice mails, appointments, and task items. The PIM application is alsoin some embodiments capable of sending and receiving data items via awireless network 710. In some embodiments, the data items managed by thePIM application are seamlessly integrated, synchronized and updated viathe wireless network 710 with the device user's corresponding data itemsstored or associated with a host computer system. As well, additionalsoftware modules, illustrated as other software module 730N, may beinstalled during manufacture.

Communication functions, including data and voice communications, areperformed through the communication subsystem 770, and possibly throughthe short-range communications subsystem 702. The communicationsubsystem 770 includes a receiver 750, a transmitter 752 and one or moreantennas, illustrated as a receive antenna 754 and a transmit antenna756. In addition, the communication subsystem 770 also includes aprocessing module, such as a digital signal processor (DSP) 758, andlocal oscillators (LOs) 760. The specific design and implementation ofthe communication subsystem 770 is dependent upon the communicationnetwork in which the mobile device 700 is intended to operate. Forexample, the communication subsystem 770 of the mobile device 700 may bedesigned to operate with the Mobitex™ DataTAC™ or General Packet RadioService (GPRS) mobile data communication networks and also designed tooperate with any of a variety of voice communication networks, such asAdvanced Mobile Phone Service (AMPS), Time Division Multiple Access(TDMA), Code Division Multiple Access CDMA, Personal CommunicationsService (PCS), Global System for Mobile Communications (GSM), etc. Othertypes of data and voice networks, both separate and integrated, may alsobe utilized with the mobile device 700.

Network access may vary depending upon the type of communication system.For example, in the Mobitex™ and DataTAC™ networks, mobile devices areregistered on the network using a unique Personal Identification Number(PIN) associated with each device. In GPRS networks, however, networkaccess is typically associated with a subscriber or user of a device. AGPRS device therefore typically has a subscriber identity module,commonly referred to as a Subscriber Identity Module (SIM) card, inorder to operate on a GPRS network.

When network registration or activation procedures have been completed,the mobile device 700 may send and receive communication signals overthe communication network 710. Signals received from the communicationnetwork 710 by the receive antenna 754 are routed to the receiver 750,which provides for signal amplification, frequency down conversion,filtering, channel selection, etc., and may also provide analog todigital conversion. Analog-to-digital conversion of the received signalallows the DSP 758 to perform more complex communication functions, suchas demodulation and decoding. In a similar manner, signals to betransmitted to the network 710 are processed (e.g., modulated andencoded) by the DSP 758 and are then provided to the transmitter 752 fordigital to analog conversion, frequency up conversion, filtering,amplification and transmission to the communication network 710 (ornetworks) via the transmit antenna 756.

In addition to processing communication signals, the DSP 758 providesfor control of the receiver 750 and the transmitter 752. For example,gains applied to communication signals in the receiver 750 and thetransmitter 752 may be adaptively controlled through automatic gaincontrol algorithms implemented in the DSP 758.

In a data communication mode, a received signal, such as a text messageor web page download, is processed by the communication subsystem 770and is input to the microprocessor 728. The received signal is thenfurther processed by the microprocessor 728 for an output to the display726, or alternatively to some other auxiliary I/O devices 706. A deviceuser may also compose data items, such as e-mail messages, using thekeyboard 714 and/or some other auxiliary I/O device 706, such as atouchpad, a rocker switch, a thumb-wheel, or some other type of inputdevice. The composed data items may then be transmitted over thecommunication network 710 via the communication subsystem 770.

In a voice communication mode, overall operation of the device issubstantially similar to the data communication mode, except thatreceived signals are output to a speaker 711, and signals fortransmission are generated by a microphone 712. Alternative voice oraudio I/O subsystems, such as a voice message recording subsystem, mayalso be implemented on the mobile device 700. In addition, the display716 may also be utilized in voice communication mode, for example, todisplay the identity of a calling party, the duration of a voice call,or other voice call related information.

The short-range communications subsystem 702 enables communicationbetween the mobile device 700 and other proximate systems or devices,which need not necessarily be similar devices. For example, theshort-range communications subsystem may include an infrared device andassociated circuits and components, or a Bluetooth™ communication moduleto provide for communication with similarly-enabled systems and devices.

In FIG. 8, the wireless device and the base stations can cooperate toimplement one or more the methods described herein. More generally, thenetwork side may be implemented by one or more network components thatmay include base stations, base station controllers, wireless routers,or mobile switching centres to name a few example. The implementationparticulars will depend on a given network configuration. In FIG. 9,microprocessor 728, RAM 718, communication sub-system (770), display726, flash memory, voice module and data module can cooperate toimplement one or more of the methods described herein. More generally,the implementation particulars will depend on a given wireless deviceconfiguration.

While the embodiments described are particularly applicable to real-timelow rate packet transmissions, such as Vol P, it is to be understoodthey can be applied to other packet transmissions that may notnecessarily be real-time or low rate, although the efficiencies realizedwith real-time low-rate applications may not necessarily be realized.

While the embodiments have been described in the context of downlinktransmission from a base station to a UE, more generally, someembodiments may be applied for the transmission from a transmitter to areceiver. The transmitter and receiver may be the base station and UErespectively in the event the embodiments are to be applied to downlinktransmission, or they may be the UE and the base station respectively inthe event the embodiments are to be applied to uplink transmission.

Numerous modifications and variations of the present application arepossible in light of the above teachings. It is therefore to beunderstood that within the scope of the appended claims, embodiments maybe practiced otherwise than as specifically described herein.

1. A method comprising: transmitting packets to a receiver using an MCS(modulation and coding scheme); receiving a plurality of NACKs (negativeacknowledgement) in respect of packets transmitted to the receiver;determining an updated MCS (modulation and encoding scheme) used totransmit subsequent packets to the receiver as a function of theplurality of NACKs.
 2. The method of claim 1 further comprising:signaling the updated MCS to the receiver.
 3. The method of claim 1wherein determining the updated MCS comprises: counting a number of theplurality of NACKs received over a time period.
 4. The method of claim 3wherein determining the updated MCS further comprises: moving to a lessaggressive MCS if the number of NACKs received over the time periodexceeds a first threshold; moving to a more aggressive MCS if the numberof NACKs received over the time period is less than a second threshold.5. The method of claim 1, wherein the MCS is adjusted independently foreach of a plurality of receivers.
 6. The method of claim 1 furthercomprising: initially assigning each of a plurality of receivers to oneof a plurality of groups of receivers, each group having a respectiveMCS; wherein moving to a more aggressive MCS for a given receiver andmoving to a less aggressive MCS for a given receiver comprises changingthe group assigned to the given receiver.
 7. The method of claim 3wherein the time period is at least 400 ms.
 8. The method of claim 3wherein the time period comprises a sliding window.
 9. The method ofclaim 1 wherein transmitting packets comprises transmitting a sequenceof VolP packets.
 10. The method of claim 1 further comprising assigningan initial MCS to the receiver based on initial feedback.
 11. The methodof claim 1 further comprising using a NACK-only signalling scheme. 12.The method of claim 2 wherein signaling the updated MCS comprises:signaling using at least one of high layer signalling, optional field ofa Media Access Control header, and physical layer signalling.
 13. Themethod of claim 1 further comprising signalling new packet notificationusing at least one of group ID, bitmap, and resource index.
 14. A methodcomprising: a receiver receiving packets over a wireless channel; thereceiver making a channel quality measurement in respect of the wirelesschannel; the receiver making an MCS adaptation decision based on thechannel quality measurement; the receiver feeding back the MCSadaptation decision in a slow rate manner.
 15. The method of claim 14further comprising: a transmitter receiving the MCS adaptation decision;the transmitter updating the MCS used for subsequent packettransmissions to that receiver in accordance with the MCS adaptationdecision.
 16. The method of claim 14 wherein the receiver feeding backthe MCS adaptation decision is performed at least every 400 ms.
 17. Themethod of claim 14 wherein the receiver feeding back the MCS adaptationdecision comprises: feeding back a first signal to indicate that a moreaggressive MCS should be used; feeding back a second signal to indicatethat a less aggressive MCS should be used; and feeding back a thirdsignal to indicate that no change in the MCS should be made.
 18. Themethod of claim 14 wherein the receiver feeding back the MCS adaptationdecision comprises: feeding back the MCS adaptation decision using atleast one of high layer signalling, optional field of a Media AccessControl header, and physical layer signalling.
 19. The method of claim14 further comprising: the receiver transmitting a NACK for each packetthat was not correctly received; the receiver transmitting nothing foreach packet that is correctly received.
 20. The method of claim 14further comprising: initially assigning each receiver to one of the aplurality of groups of receivers, each group having a respective MCS;wherein moving to a more aggressive MCS for a given receiver and movingto a less aggressive MCS for a given receiver comprise changing thegroup assigned to the receiver.